Gu ms, Resins, 



ferences occur, both as to size of tree and 

 yield of latex, under similar cultural 

 conditions, the results obtained from 

 individual trees do not form satisfactory 

 evidence upon which to base a conclusion 

 as to the average yield of many thousands 

 of trees of like age. Hence, trial tappings 

 of single trees, or groups of limited 

 number, of equal age vary very consi- 

 derably. Thus, we have trees, or groups 

 of trees, producing 1, 2 and 3 oz. of 

 rubber, others ranging as high as from 4 

 to 6 oz. at one tapping. With such vari- 

 able data to go upon, the difficulty of arri- 

 ving at atrue average yield for a planting 

 of perhaps half a million trees is obvious. 



Tentative experiments made in this 

 district would indicate that trees grown 

 under the most favourable conditions of 

 soil, &c, may be tapped twice a year 

 with equal results ; but it would seem 

 premature to say with assurance that 

 the trees covering a large area could be 

 safely subjected to such a drain upon 

 their vitality until they had attained a 

 greater age. To repeat, however, selected 

 groups of trees of the age above men- 

 tioned have withstood a second tapping 

 in a year without visible injury. 



With regard to local soil conditions, it 

 has been stated that " the oldest portion 

 of the Isthmus evidently began its 

 superaquatic existence at a compara- 

 tively recent period— geologically speak- 

 ing "*- and that much of the geolo gical 

 formation of the Eastern Atlantic 

 versant of the Mexican cordillera to- 

 wards the Isthmus of Tehuantepec is of 

 similar late origin is indicated by the 

 presence of stratifications of marine 

 shells and primordial ooze, where sub- 

 sequent aqueous erosions have occurred, 

 creating, in the cycle of topographic 

 changes, more or less abrupt undulations, 

 ridges and valleys, with occasional hills 

 reaching to a height of 150 ft. between 

 depressions. In the immediate neigh- 

 bourhood of the sea and the riverine 

 estuaries alluvial deposits are found, but 

 these have proved unsuitable for most 

 cultural purposes, owing to the shallow- 

 ness of the water basin. On the approach 

 to the sierras, "mesas," or benchlands, 

 occur of an entirely different structure, 

 these being made up of granitic or other 

 primitive detritus, incorporated with 

 abundant vegetable matter. Such lands, 

 unfortunately, are not encountered in 

 any large areas. The soil of the district 

 herein referred to is composed of clayey 

 loams, overlaid in parts with beds of rich 

 black humus of the greatest fertility. 



* " Report of Explorations and Surveys for a 

 Ship Canal by the way of the Isthmus of 

 Tehuantepec." By Robert W. Shufeldt, 

 Captain, United States' Navy. Washington, 

 1872. 



6 [January, 1909, 



The climate of the Atlantic side of the 

 Isthmus of Tehuantepec has three well- 

 defined seasons -namely, the wet season 

 Proper, commencing usually the last week 

 ] n May or the first week in June, and con- 

 tinuing till the end of October ; the lighter 

 wet or "norther" season, extending 

 over the months of November, December, 

 January and February; and the dry 

 season, comprising the months of 

 March, April, and May. The annual 

 rainfall is between 90 and 120 inches, 

 with a very favourable distribution, 

 three-fourths of the total precipitation 

 taking place between June and October, 

 while from then on until the approach 

 of the dry season frequent showers fall, 

 with much mist and drizzle. No month 

 of the year is wholly free from rain, 

 occasional light showers occurring even 

 during the height of the dry season, 

 when the greatest heat of the year is 

 experienced, the Mercury fluctuating 

 between 80° and 90° F. in the shade, and 

 sometimes marking 100°. An appreciable 

 diminution in temperature ensues dur- 

 ing the wet months, the average range 

 being from 75 to 85° F., while during 

 the cooler months, from November 

 to February, the average temperature 

 is between 60 and 80° F., once in a while 

 falling as low as 55° F. in the early hours 

 of the morning. The lowest temper- 

 ature recorded by one observer over a 

 period of nine years was 50° F., this 

 occurring in the month of January. The 

 relative salubrity of the climate of the 

 Isthmus of Tehuantepec as a whole, as 

 compared with that of similar latitudes 

 elsewhere, is quite remarkable, this 

 continent being cooler under the equator 

 than any other, owing to the expanse 

 of sea surrounding it and the more 

 elevated configuration of the land. 



The vegetation of this region presents 

 to the trained eye a strictly tropical 

 aspect, the forest growth consisting 

 almost entirely of tropical genera, such 

 as mahogany, Spanish cedar, lignum 

 vitae, giant representatives of the ficus 

 family, the stately ceiba, with its wide- 

 spreading, buttressed trunk ; numerous 

 examples of sapotaceous trees, includ- 

 ing the lofty " Mame" and the " chicle " 

 (from which American "chewing-gum" 

 is made, and which also produces one 

 of the best of all wild tropical fruits, 

 namely, the "zapodillo," or, in the verna- 

 cular "chico zapote") ; while many ano- 

 naceous trees occur, some of which bear 

 edible fruits— close relatives of the 

 famous custard apple, or " chirimoya." 

 Hard-wooded shrubs of various orders, 

 and large-leaved plants from the under- 

 growth, with scattered groups of deli- 

 cate slender-stemmed palms, belonging 

 principally to the genus Chamoedorea. 



